Improving the efficiency of any internal combustion engine can help to reduce the fuel consumption of the engine and thereby reduce running costs and the cost to the environment from harmful engine emissions. Many fuel efficiency measures have been developed recently but most of these concentrate on the way fuel is delivered to the engine and maximizing the work done by the fuel supplied to the engine. Other measures can however be taken to reduce the strain placed on the engine, for example in a car, limiting the speed of acceleration or increasing gear ratios at higher speeds.
Internal combustion engines use oil to lubricate the moving parts of the engine, reducing the friction between these parts and thereby increasing the working life of the moving parts. As the temperature of the oil increases, the oil becomes thinner and so provides the moving parts with less physical protection but at these increased temperatures, typically 60 to 80° C., additives in the oil start are activated and provide the necessary protection. These additives include anti-wear additives that are laid down on the internal surfaces of the engine at its components at 60° C. and hotter. The oil is also used to help cool components of the engine.
The temperature of the oil must be controlled, in particular to control the viscosity of the oil and so also its effectiveness to properly lubricate the moving parts of the engine. It is known that an engine whose parts, in particular the moving parts, are warm, and is more fuel efficient and the moving parts are less susceptible to damage.
The temperature of the oil in a hybrid vehicle can be a particular problem. A hybrid engine is designed to be efficient and as such generates less heat than a conventional engine. The temperature of the oil in a hybrid engine may therefore not be high enough to ensure the engine runs efficiently.
The oil in an internal combustion engine is normally heated by the engine itself but it is known to separately heat the oil using a conventional heater. This conventional type of heater may be a heating rod or plug that directly heats the oil. This is a relatively simple and therefore cost effective method of heating the oil but there are disadvantages. The rod or plug must be hot enough to transfer enough heat to the oil to raise the temperature of the oil in a reasonable period of time, but then the rods or plugs may cause the oil to burn when in contact with the rods or plugs. This may damage the composition of the oil and may be a potential source of fire.
In an alternative solution, a primary and secondary circuit is used. Water in the secondary circuit is used to heat oil in the primary circuit. In a further alternative solution, oil in a chamber is heated using heat provided by the exhaust gases from the engine.
It is desirable to provide an alternative way to heat the oil in an internal combustion engine.